There's a good amount of subjectivity regarding baseball prospects. With the evaluation of talent being in the eye of the beholder, finding consensus is often difficult. Even Jim Callis and Jonathan Mayo at MLBPipeline.com don't always see eye-to-eye on everything. They'll be discussing their viewpoints regularly in a feature called "Pipeline Perspectives." To submit a topic for them to debate, click here.

Which recently called up pitching prospect will have the biggest impact on the pennant races?

While my colleague Jim Callis makes the case for the A's Sonny Gray, I kindly submit that it's St. Louis' Michael Wacha who will have the greatest impact down the stretch.

Sunday's start against the Pirates was Wacha's last against one of the National League Central's contenders. But he cemented his spot as the No. 5 man in the rotation for September after tossing six shutout innings against the Reds, then followed that up with seven more scoreless frames against the Pirates. As a result, he still could get as many as four more starts. A game and a half separates the three top teams in the division, so it doesn't take a sabermetrician to figure out what kind of impact Wacha can have during the season's final stretch. Or beyond. Assuming the Cardinals shorten their rotation come postseason-time, Wacha has shown he can be a very viable weapon coming out of the bullpen if needed.

The Cardinals' place in the postseason might seem all but guaranteed, but there's still plenty to figure out atop the NL Central as the Cards jockey for position with the Reds and Pirates. There is a big difference between making it to the one-and-done Wild Card game and winning the division, thus guaranteeing a full playoff series, at the very least. Wacha has the opportunity to make a big difference in St. Louis' postseason positioning.

Ranked No. 15 overall and No. 2 on the Cardinals' Top 20, Wacha was called upon to help out on previous occasions. He made three starts in late May/early June, then did some fine work in August, mostly out of the bullpen.

During Wacha's very quick ascent to the big leagues -- the 2012 first-rounder made his full-season debut all the way up in Triple-A after an absolutely dominant Spring Training -- he's thrown a combined 131 1/3 innings. That might sound like a good amount for a player just beginning his pro career, perhaps even a time where an organization thinks about shutting a guy down. But Wacha came into the organization as a durable right-hander, one who threw nearly 130 innings as a sophomore at Texas A&M, then 137 1/3 between his junior year and his pro debut last summer. They also used a six-man rotation in Triple-A when he was in the Minors and kept him largely to relief work when he was up in the Majors previously. So don't worry about Wacha wearing down.

Case in point: Wacha was up to 93 mph in his final inning of work against the Reds on Sept. 3 and was still touching 95 mph in the seventh inning against the Pirates. He relies heavily on his fastball and his changeup, which is his best secondary offering. He folds in enough breaking stuff to keep hitters honest, giving him a three-pitch mix that should continue to allow him to be very effective down the stretch.

Jonathan Mayo is a reporter for MLB.com and writes a blog, B3. Follow @JonathanMayoB3 on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.